Calutron cathode interlock circuit



May 25, 1959 l.. w. BALDWIN 2,888,563

cALUTRoN cATHoDE INTERLocK CIRCUIT 2 Sheets-Sheet 1 Filed May 14, 1946 Inn/Emol#` LAWRENCE. W. BALDWIN ATTORNEY May 26, 1959 L. w. BALDWIN cALuTRoN cATHoDE INTERLocK CIRCUIT 2 Sheets-Sheet 2 Filed May 14, 1946 lNvaNToR LAWRENCE W. BALDWIN ATTORNEY United States Patent O CALUTRON CATHGDE INTERLOCK CIRCUIT Lawrence W. Baldwin, San Diego, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application May 14, 1946, Serial No. 669,482

2 Claims. (Cl. Z50-41.9)

This invention relates to a protective circuit for the cathode of a calutron.

An object of the invention is to provide a circuit arrangement for preventing the application of the arc voltage to an ion source of a Calutron until after the electron emitting cathode has been brought up to operating ternperature.

This invention is particularly adapted for use with a calutron of the type disclosed in U. S. Patent No. 2,709,222 issued May 24, 1955 to E. O. Lawrence for Calutrons.

Referring to the drawing briefly,

Fig. l is a wiring diagram of an embodiment of this invention; and

Fig. 2 is a wiring diagram of another embodiment of this invention.

Referring to the drawing in detail a calutron 100 of the type disclosed in the aforesaid Lawrence patent is shown schematically and this calutron is provided with an ion source having a cathode K.

In order to obtain the maximum life from the cathode K it is advisable to allow it to be heated for a brief period of time before any attempt is made to strike an arc. If this is not done the positive ion bombardment of the cathode K increases the possibility of developing hot spots on the surface of the cathode K thereby causing undue erosion of the cathode K. Even a slight erosion of the cathode K, because of the cumulative effect, will appreciably shorten its total life.

In actual practice, when striking an arc, the cathode K is operated space charge limited and the cloud of electrons that surrounds the cathode K protects it from positive ion bombardment. By heating the cathode K and establishing this cloud of electrons about it prior to striking the arc, it is effectively shielded from positive ion bombardment.

Figure 1 shows a very simple circuit involving a time delay relayTDR interlocking the cathode K supply 1 and the arc voltage supply 2. Inasmuch as the arc voltage supply 2 shown requires that the filaments of the rectier tubes be heated in advance for a certain period of time and that the filament supply 3 must be energized before A.C. voltage is applied to the arc voltage supply 2, it is possible to combine the two time delay functions and use only a single time delay relay TDR.

Figure 2 shows a circuit for a J-K time delay relay interlock. In this figure the push button and relay circuits for turning on the various power supplies have been represented by simple switches which perform the same function.

More particularly from Fig. 2 it is clear that it is possible to turn on the cathode K supply 11 by operation of switch S1 independently of any other power supplies so long as the ion source cooling water is flowing through the pipes M and flow switch FS. It is also possbile to turn on the filament supply 12 for the arc voltage supply 13 and the lament supply 14 for the J-K regulator 15 as a group independent of any other circuit by operation of switch S2. However, when the cathode K supply 11 is first turned on the J-K regulator 15' cannot be in operation because of the interlocks including time delay relay TDR1 and for this reason the saturable reactor SR has its maximum impedance at this time and a reduced voltage lower than any normal operating voltage is applied to the cathode K. The regulator 15 is of the type disclosed in the copending application of Robert De Liban, since isused as U.S. Patent No. 2,745,964 on May l5, 1956, and entitled Arc Regulator for Calutron Ion Source. This operation is of particular advantage inasmuch as when the cathode K is rst turned on, it is cold and otherwise would receive a very large surge of current. Such a large surge of current in a concentrated magnetic field would result in undue mechanical shock.

At the same time that the cathode K supply 11 is originally energized, time delay relay TDR1 is energized which causes its contacts to close after a certain short predetermined time delay. This time delay, however, is sufficiently long to allow the temperature of the cathode K to reach an equilibrium at the reduced current value.

As mentioned the switch S2 for the filament supplies 12 and 14 can be closed independently. In actual practice it was usually closed before the cathode K supply switch S1. In order to protect the rectifier tubes in the arc voltage supply 13, time delay TDR2 is provided. This relay TDR2 allows the filaments of the rectifier tubes in the arc voltage supply 13 to heat to their operating temperature before plate voltage can be applied to them. The time delay required for this operation is several minutes for the type of tubes customarily used. Closing of switch S2 also applies filament power to the various tubes in the J-K regulator 15, allowing their filaments to come to operating temperature, although this of course requires much less time.

Now, if the J-K filaments and the cathode K supply filaments are turned on and sufficient time has elapsed for time delay relay TDR1 to operate, then plate voltage is supplied to the I-K regulator 15. At this point no arc current will yet be flowing because it has been impossible so far to energize the plate supply of the arc voltage supply rectifier. Therefore, the J-K regulator receives no input signal from the current transformer CT. For this reason a maximum current flows through the D.C. windings of the saturable reactor SR, reducing its impedance to a minmum and thus heating the cathode K to its maximum or normal operation temperature. This will produce the necessary cloud of electrons to prevent positive ion bombardment of the cathode K when the first attempt is subsequently made to strike an arc.

If both the time delay relay TDR1 and time delay relay TDR2 have operated and their time delays have elapsed, then the arc voltage supply switch S3 can be closed, applying plate voltage to the arc voltage supply which will apply a D.C. arc voltage to the tank causing the arc to strike. This will even occur automatically at the proper time if switch S3 was previously closed. The flow of A.C. current in the plate circuits of the arc voltage supply 13 causes a signal to be transmitted through the current transformer CT to the J-K regulator 15, reducing the voltage to the cathode K and regulating the arc discharge. It is also possible to control the I-K regulator by means of a D.C. signal voltage appearing across a resistance in one of the output leads of the arc voltage supply.

The arrangement described avoids mechanical shock to the cathode K, thermal shock to the cathode K, and positive ion bombardment of the cathode K during the initial period of operation. Turning on the cathode K at a reduced value has the additional advantage of testing the circuit before placing it in operation.

What is claimed is:

1. In a calutron having an evacuated tank, an ion a thermally emissive cathode disposed in said tank adjacent said arc block, a source of alternating current power, a cathode supply circuit operatively connected to said thermally emissive cathode, an arc voltage supply operatively connected between said thermally emissive cathode and said arc block, rst and second control means, a time delay relay adapted to prepare said second control means for operation, means controlled by operation of said first control means for connecting said cathode supply circuit to said source of alternating current power and for operating said time delay relay whereby said second control means is prepared for operation after a predetermined time subsequent to tne operation of said rst control means, and means controlled by operation of said second control means for connecting said arc voltage supply to said source of alternating current power.

2. In a calutron having an evacuated tank, an ion source comprising an arc block disposed in said tank, a thermally emissive arc cathode disposed in said tank adjacent said arc block, a source of alternating current power, an arc cathode supply circuit operatively connected to said arc cathode, an arc voltage supply operatively connected between said arc cathode and said arc block, said arc voltage supply having a cathode heating circuit and an anode circuit, an emission regulator circuit responsive to the amplitude of alternating current supplied to the vanode circuit of said arc voltage supply adapted to control the alternating current power supplied to said arc cathode supply circuit whereby the current owing between said thermally emissive cathode and said arc block is maintained substantially constant, said emission regulator circuit having a cathode heating circuit and an anode circuit, rst, second, and third control means, means controlled by operation of said first control means for supplying alternating current power to the cathode heating circuit of said arc voltage supply and to the cathode heating circuit of said emission regulator circuit, means controlled by operation of said second control means for connecting said arc cathode supply circuit to said source of alternating current power, means including time delay relay means controlled `by operation of both said first and second control circuits for connecting the plate circuit of said emission regulator to said source of alternating current power and for preparing said third control circuit for operation, and means controlled by operation of said third control circuit for connecting the plate of circuit of saidl arc voltage supply to said source of alternating current power.

Whitney kMay 29, 1934 Simon et al Dec. ll, 1934 

